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Rim-Differentiated C5‑Symmetric Tiara-Pillar[5]arenes

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journal contribution
posted on 08.12.2017, 00:00 by Minjie Guo, Xuemei Wang, Caihong Zhan, Paul Demay-Drouhard, Wenjiao Li, Ke Du, Mark A. Olson, Han Zuilhof, Andrew C.-H. Sue
The synthesis of “rim-differentiated” C5-symmetric pillar­[5]­arenes, whose two rims are decorated with different chemical functionalities, has remained a challenging task. This is due to the inherent statistical nature of the cyclization of 1,4-disubstituted alkoxybenzenes with different substituents, which leads to four constitutional isomers with only 1/16th being rim-differentiated. Herein, we report a “preoriented” synthetic protocol based on FeCl3-catalyzed cyclization of asymmetrically substituted 2,5-dialkoxybenzyl alcohols. This yields an unprecedented 55% selectivity of the C5-symmetric tiara-like pillar[5]­arene isomer among four constitutional isomers. Based on this new method, a series of functionalizable tiara-pillar[5]­arene derivatives with C5-symmetry was successfully synthesized, isolated, and fully characterized in the solid state.